Hydrophobic and Hydrophilic Interactions

The term hydrophobic interaction unfortunately implies some form of molecular repulsion, which, outside the van der Waals radii of a molecule, is quite impossible. The term hydrophobic force literally means fear of water force. The term hydrophobic has been introduced as an alternative to dispersive but means the same. It is not clear from the literature how the word hydrophobic originated, but it may have been provoked by the immiscibility of a dispersive solvent such as n-heptane with a very polar solvent such as water. 

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The term hydrophilic force , literally meaning love of water force, was introduced as a complement to hydrophobic force . Hydrophilic forces are equivalent to polar forces, and polar solvents that interact strongly with water are called hydrophilic solvents. 

Short Aliphatic Chains Offering Weak Dispersive Interactions 

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In view of the importance of the particle/bubble contact, it may be assumed that the stress acting on the particles during gas sparging is determined by electrostatic interactions as well as by hydrophobic and hydrophilic interactions, which are determined by the nature of the liquid/solid system. The use of Pluronic as additive leads to the reduction of destruction process [44,47] possibly due to less bubble/floc contact which is also described by Meier et. al. [67]. 

This result makes it clear that particle stress is strongly dependent on the interaction between the particles and the interface, so that electrostatic and also hydrophobic and hydrophilic interactions with the phase boundary are particularly important. This means that the stress caused by gas sparging and also by boundary-layer flows, as opposed to reactors with free turbulent flow (reactors with impellers and baffles), may depend on the particle system and therefore applicability to other material systems is limited. 

There is a second long interface stretching between the threefold and fourfold axes, involving both hydrophobic and hydrophilic interactions. Close to the threefold axis is an intersubunit salt bridge between Asp-139 of subunit I and His-128 in III, which links the N-terminal end of helix D (III) to a position near the kink in helix D (I). Further along the interface, N-terminal residues 6-12 of subunit III make several interactions with the C-helix of subunit I, including several which are mediated... 

Gabrielska, J., Sarapuk, J. and Przestalski, S. (1997). Role of hydrophobic and hydrophilic interactions of organotin and organolead compounds with model lipid membranes, Z. Naturforsch. C., 52, 209-216. 

Factors which influence properties chain length, branching vs. linear, nature of the monomer, density, interchain bonds, hydrophobic and hydrophilic interactions. 

The term generation describes the number of times arms have been extended. The nature of each generation can be varied so that mixtures of steric requirements and hydro-phobic or hydrophilic character can be introduced offering materials with varying structures and properties. By varying the hydrophobic and hydrophilic interactions and steric nature of the arms secondary and tertiary structural preferences can be imposed on the dendrimer. 

Figure 25-15 Stationary phases for hydrophobic and hydrophilic interaction chromatography...

Hydrophobic and Hydrophilic Interactions. Although proteins are generally soluble in water or dilute salt solutions, they contain many amino acids with aliphatic or aromatic side-chain residues that have low solubility in water, apparently because of... 

The major physical forces, which help the membrane to maintain their structure, consist of hydrophobic and hydrophilic interactions, electrostatic forces, and van der Waals interactions. The main driving force for formation of the bilayer originates from the hydrophobic interactions and van der Waals interaction forces between hydrocarbon chains of the hpid molecules. The hydrophobic forces control the order and packing of hpids and electrostatic interactions between the polar head groups and their interaction with water molecules contribute to bUayer stabUization. The bUayer is continuous and it exhibits semirigid properties. The fluid nature of the membrane is governed by the hpid composition and the namre of the forces that exist between the constituent hpids and proteins. Due to fluid hpid bilayer, the diffusion constant for a phosphohpids is 1 m /s,... 

The crystal structure of an aralkylated tripeptide is presented in Figure 15.9. This molecule contains regions that are hydrophobic, while others are hydrophilic. These areas segregate in the crystal structure as shown, and water adds in order to stabilize the hydrophilic areas. Often, however, the distinction between hydrophobic and hydrophilic interactions is not so clear. 

The theories outlined above are general and pertain to any nucleation processes within a melt. The H20 system is of particular interest to us for a number of reasons (1) the hydrogen-bonding capabilities of these molecules, (2) the hydrophobic and hydrophilic interactions of biomaterials, and (3) the absolute requirements for water in living systems. Consequently, freezing of H20 from the liquid phase is of special significance for biological systems. 

Folding is a consequence of the hydrophobic and hydrophilic interactions between residues lying in different parts of the primary structure. One important link responsible for tertiary structure is the disulfide link (-S-S-) between amino acids containing sulfur. 

A. 19.3 While the best model depends on the question being investigated, the Stern model would provide a more accurate model of the interphase because it considers molecular size and non-electrostatic molecular absorption, both of which are very important to biological systems. For example, proteins control the flow of ions through membranes based on size, so if size isn t considered, the interactions leading to flow control would be missing an essential component. Hydrophobic and hydrophilic interactions are also an important part of interphase interactions. 

The fine balance between hydrophobic and hydrophilic interactions, as well as major steric requirements, play important roles in the binding of inhibitors. Cyanide is the only ligand that may bind in a 2 1 ratio. It is likely that the bis-cyanide adduct has the same arrangement as the NCS —H2O derivative. The spin state of the bis-cyanide adduct is S = 2. ... 

The first X-ray studies on a Cu2Zn2SOD were performed by the Richardson group over the decade 1972-1982 on the enzyme from bovine erythrocytes (37-40) and resulted in a structure refined at 2.0 A resolution (41a). The Cu2Zn2SOD dimers from bovine er3rthrocytes are made of two subunits of identical amino acid composition, each containing 151 residues. The crystal structure has revealed that the two monomers are related by an almost exact, noncrystallographic twofold axis. The monomers show extensive contact mediated by hydrophobic and hydrophilic interactions that involve about 9% of the total monomer surface (4Ia) (see Section II,A,5). 

The phenomenon of the rapid adsorption of albumin onto a PEUN surface may be associated with hydrophobic and hydrophilic interactions of the PEUN surface with some sequences of relatively hydrophobic amino acid residues in the interior of albumin. An albumin molecule is composed of three-subdomains (15). There are two gaps between the subdomains. One is a hydrophobic pocket with an affinity constant, K3=1.1x10 M for stearic acid the other is an intermediate hydrophobic pocket with K =1.5xl0 M for bilirubin (16). Perhaps the structure of adsorbed albumin in contact with a PEUN surface is composed of hydrophobic and hydrophilic regions corresponding or complementary to those of the PEUN surface, even though the exterior of native albumin is rich in hydrophilic amino acid side chains. 

Hydrophilic interaction is operative not only in solvating small rigid ions, but also in stabilizing extended structures such as DNA, proteins, and inorganic extended surfaces such as silica, mica, and zeolites. In the first two examples (proteins and DNA), both hydrophobic and hydrophilic interactions operate synergistically to stabilize the structure. In the case of several common extended objects such as silica and mica surfaces [1,2], it is primarily the hydrophilic interaction that dominates. 

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